The present invention pertains to the practice of high pressure liquid chromatography in which a chromatographic column is connected by suitable conduit to a reciprocating type pump operable to transmit a liquid vehicle from a supply reservoir, through a pulse damper which embodies the present invention, the liquid then being carried to an injection valve where a liquid sample to be processed is entrained in the liquid vehicle, following which said sample is transmitted through the column for determination of the constituents of the sample being processed. The liquid vehicle usually is a suitable chemical solvent which is non-reactive with the sample which is entrained therein and neither the liquid vehicle or sample are chemically reactive with the material with which the test column is packed in accordance with the usual practice of chromatography.
In such systems, the solvent flow paths should have minimum internal volume and be well swept so as to afford continuous movement of the liquid solvent and test material through the system and is important in solvent changeover and when using gradient chromatography techniques. If excessive internal volume exists, it tends to cause mixing which is detrimental to efficient solvent changeover and causes loss of predictable time-based solvent proportions in gradient work.
Various types of pulse dampers have been developed heretofore for certain purposes. For example, prior U.S. Pat. No. 3,333,604, to Birdwell, dated Aug. 1, 1967, discloses a pulsation reducer primarily adapted for use with car washing equipment in which relatively high pressure fluid systems are desired. A pair of disks which are slightly concave are bolted together to clamp a flexible diaphragm adjacent one side of a cavity, one of the disks having openings therein for application of fluid under pressure against one face of the diaphragm and pneumatic pressure is provided in the cavity to react against the diaphragm and absorb pulsations imposed upon the same by fluid being pumped by a reciprocating type pump.
One example of a chromatography system in which a pulse damper is included forms the subject matter of prior U.S. Pat. No. 3,984,315, to Ernst et al, dated Oct. 5, 1976, and in which the chromatographic column is in circuit with a pulse damper in which a flexible diaphragm is mounted at one side of a cavity through which the test liquid flows against one face of the diaphragm and the opposite face thereof has a coil spring imposed in a manner to resist the flexing of the diaphragm as pulsations from a pump discharge liquid thereagainst.
Several additional prior U.S. Pat. Nos. 4,163,461 to Jacobellis, dated Aug. 7, 1979, and 4,186,776 to Burton, dated Feb. 5, 1980, respectively show somewhat bulbous shaped cavities in which flexible diaphragms are disposed midway thereof for application of fluid pumped by a reciprocating pump against one face, while the portion of the cavity adjacent the opposite side of each diaphragm respectively contains gas under pressure, and a compressible fluid which appears to be gaseous as distinguished from a liquid.
There also is another type of pulse damper employed in systems for high pressure liquid chromatography, such as shown in prior U.S. Pat. No. 4,222,414, to Achener, dated Sept. 16, 1980, and in which a plastic spool made from material which is chemically inert with respect to fluids typically used in liquid chromatography is provided with an axial bore adequate in size to receive liquid delivered thereto upon each reciprocation stroke of the pump of the system, the spool preferably being formed from polytetrafluoro-ethylene, one type of which is sold under the trademark TEFLON. The spool is encased within a cylindrical housing which preferably is made from stainless steel and an annular chamber surrounds the spool and is filled with what is stated to be a compressible liquid but no specific type of compressible liquid is described.
In regard to the type of pulse damper disclosed in the above identified patent, it is known that an irremedial defect exists when used in high pressure chromatography systems in that, the bore size, and therefore the internal volume, must be predicated on the sensitivity, displacement per p.s.i., desired, and the resultant stress level. As the bore diameter tends to zero, the stress levels in the compliant tube approach infinity. For practical levels of stress, to avoid non-plastic deformation, the bore size for a practical device, and therefore the minimum internal volume, must be much greater than that necessary for mobile phase flow considerations.
The pulse damper comprising the present invention is a relatively simple device, highly effective in operation, and comprising distinct improvements over the prior art devices referred to hereinabove and details of which are set forth below.